The world is experiencing the most abrupt shift in human settlements in history. After decades of rural to urban migration, half of all humanity now lives in cities. By 2050, that figure will surge to 75 percent, with the developing world responsible for most of this increase. Mankind's unprecedented urbanization will create new economic opportunities. But it will also place extraordinary strains on national and municipal authorities struggling to provide the poor inhabitants of these chaotic agglomerations with basic security, sustainable livelihoods, and modern infrastructure.
And when it comes to natural disasters, today's burgeoning urban centers will increasingly be on the front lines.
Statistics on urbanization are staggering. Cities in the developing world are adding five million residents per month--seven thousand each hour, or more than two per second. For perspective, this is the equivalent to adding one city the size of the United Kingdom every year. Between 2010 and 2050, experts predict, Africa's urban population will triple, while Asia's will double. The vast majority of newcomers are poor. Today, some 828 million people live in slums,including more than 60 percent of city-dwellers in sub-Saharan Africa (and 43 percent in South-Central Asia). By 2040, the global number of slum-dwellers will climb to two billion--nearly a quarter of humanity--as the world's shanty-towns,bidonvilles, and favelas add another twenty-five million per year.
From a long-term economic perspective, the shift from rural to urban living can be a boon for national wealth. As a general rule, UN Habitat explains, "The more urbanized a country, the higher the individual incomes."